Yeah, when I was leak testing it I was pouring about a gallon at a time so that it would fill the sink and give a little bit of pressure as it was draining. It was a little slow but I think because its a straight shot down to the ground it doesnt create to much suction and lets it drain pretty easy. I think just letting the water run while washing hands it will drain and not even build up.

Thinking of the 1.5 to garden hose issue... My neighbor has a sump pump discharging through a garden hose... The fittings exist. I can't get a pic of it as I'm at work and the pump is underground at home.